Method and apparatus for securing an electrically conductive interconnect through a metallic substrate

ABSTRACT

A method for securing an electrically conductive interconnect ( 30 ) through a metallic substrate ( 36 ) having a first surface ( 36 ) and a second surface ( 38 ). The method may include the steps of: forming a hole ( 34 ) in the metallic substrate ( 36 ), the hole ( 34 ) defined by an internal surface ( 46 ) of the metallic substrate ( 36 ) that extends from the first surface ( 36 ) to the second surface ( 38 ) of the metallic substrate ( 36 ); applying an electrically insulating layer ( 48 ) to the metallic substrate ( 36 ) including at least the first surface ( 36 ), the second surface ( 38 ), and the internal surface ( 46 ); applying a solderable coating ( 50 ) to at least a portion of the electrically insulating layer ( 48 ) on the second surface ( 38 ) of the metallic substrate ( 36 ) around the hole ( 34 ); applying a solder (52) to at least a portion of the solderable coating ( 50 ) at and above the hole ( 34 ); inserting the interconnect ( 30 ) through the hole ( 34 ); and solder bonding the interconnect ( 30 ) within the hole ( 34 ). Additionally, there is a module that incorporates the method.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is related to the following co-pending andcommonly assigned patent application, which is hereby incorporated byreference herein: application Ser. No. ______, entitled “Method andApparatus for Securing a Metallic Substrate to a Metallic Housing,”filed on same date herewith, by Ying Wang and Thomas P. Gall, attorney'sdocket number AP01993.

FIELD OF THE INVENTION

[0002] This invention in general relates to electronic circuits mountedon metallic substrates and, more particularly, to a method and apparatusfor securing an electrically conductive interconnect through themetallic substrate.

BACKGROUND OF THE INVENTION

[0003] Engine mounted electronic control modules for vehicular enginesare subject to a high level of heat and vibration. In theseapplications, electronic components and circuits are formed on ametallic substrate that typically needs to be enclosed within a sealedmetallic housing. In the past, it has been difficult and costly toelectrically connect the internally enclosed electronic components andcircuits to external devices.

[0004] Providing a through-hole to electrically connect circuits hasbeen used on ceramic and fiberglass substrates or boards. However, theseschemes do not address electronic devices that have thermally conductivemetallic substrates such as aluminum. When using a metallic substrateand within a metallic housing, care must be taken so as to electricallyinsulate any components and connectors from the metallic substrate andhousing.

[0005] For metallic substrates, prior methods have extended a pluralityof pins through a single window opening in the metallic substrate. Aninsert-molded lead frame extends through the window opening and providesisolation between the plurality of pins. A series of wire bonds are thennecessary to connect the pins to the electronic circuit on the metallicsubstrate. Moreover, a separate special plating process is typicallyrequired on the metallic substrate for the circuits and components. Theuse of wire bonds and plating process, however, increases the complexityof the manufacturing process and, accordingly, increases the cost of themodule.

[0006] An interconnect within a through-hole has been used for steelsubstrates on voltage regulators. The through-hole in that application,however, is glass sealed and still requires the use of wire bonds toconnect the interconnect to the circuit on the metallic substrate.

[0007] In sum, current devices and methods to connect electroniccomponents and circuits through a metallic substrate are costly.Accordingly, there is a need for improved ways to provide aninterconnect approach that reduces the complexity of the manufacturingprocess and reduces costs. This is especially important in high volumeapplications such as electronic control modules for vehicles. Moreover,new interconnect approaches should take advantage of lower cost metallicsubstrates such as aluminum.

[0008] It is, therefore, desirable to provide an improved device andmethod of securing an electrically conductive interconnect through ametallic substrate to overcome most, if not all, of the precedingproblems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a perspective view of an electronic control moduleaccording to one embodiment of the present invention;

[0010]FIG. 2 is an exploded view of the electronic control module inFIG. 1.

[0011]FIG. 3 is a perspective view of one metallic substrate of thepresent invention.

[0012] FIGS. 4A-4F are cross-sectional views of a metallic substrateillustrating one embodiment of a method of the present invention thatforms an interconnect device through the metallic substrate.

[0013] FIGS. 5A-C are cross-sectional views of a metallic substrate andhousing illustrating one embodiment of a method of the present inventionthat attaches the metallic substrate to the housing.

[0014] While the invention is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. However,it should be understood that the invention is not intended to be limitedto the particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

[0015] What is described is a method and apparatus for securing anelectrically conductive interconnect through a metallic substrate. Forpurposes of illustration, an example of the method and apparatus will bedescribed in the context of an electronic control module for a vehicle.However, the present invention is not limited to modules for vehiclesbut may also apply to other housings or devices where electricallyconductive interconnects are needed through a metallic substrate.

[0016] To this end, generally, in one embodiment there is a method forsecuring an electrically conductive interconnect through a metallicsubstrate having a first surface and a second surface. The method mayinclude the steps of: forming a hole in the metallic substrate, the holedefined by an internal surface of the metallic substrate that extendsfrom the first surface to the second surface of the metallic substrate;applying an electrically insulating layer to the metallic substrateincluding at least the first surface, the second surface, and theinternal surface; applying a solderable coating to at least a portion ofthe electrically insulating layer on the second surface of the metallicsubstrate around the hole; applying a solder to at least a portion ofthe solderable coating at the hole; inserting the interconnect throughthe hole; and solder bonding the interconnect within the hole.

[0017] Another embodiment of the present invention includes a modulehaving a connector and a metallic substrate. The connector has aconnector housing and a plurality of electrically conductiveinterconnects. The metallic substrate has a plurality of holes, a firstsurface, a second surface, and an electrically insulating layer. Theinsulation layer is formed on at least the first surface, the secondsurface, and within the plurality of holes. Each interconnect thenextends through a separate hole in the metallic substrate and isattached to the insulating layer of the metallic substrate by asolderable coating and a solder.

[0018] In a further embodiment, the present invention includes anelectronic control module for a vehicle having a connector and ametallic substrate. The connector has a connector housing and aplurality of electrically conductive interconnects. The metallicsubstrate has a plurality of holes, a first surface, a second surface,and an electrically insulating layer. The insulating layer is formed onat least the first surface, the second surface, and within the pluralityof holes. In this embodiment, the electronic control module also has ameans for securing the plurality of interconnects to the metallicsubstrate to provide a hermetic seal. Additionally, the electroniccontrol module has a means for electrically connecting the plurality ofinterconnects to components and circuitry on the metallic substratewithout the use of wire bonds.

[0019] Now, turning to the drawings, an example use of a method andapparatus will be explained in the context of an electronic controlmodule for a vehicle. FIG. 1 shows an electronic control module 20. Inone embodiment, generally, the electronic control module 20 has aconnector 22, a metallic substrate 24, and a module housing 26.

[0020] The connector 22 includes a connector housing 28 and a pluralityof electrically conductive interconnects 30. The interconnects 30 maytake a variety of forms but, in one embodiment, may be cylindricalmetallic pins.

[0021] The substrate 24 is made of a metallic material. In oneembodiment, the substrate 24 is made of aluminum. Aluminum is lessexpensive than other metallic materials and is a good conductor of heatthat is important for automobile applications. The metallic substrate 24is used for mounting the components and other circuitry for theelectronic control module 20.

[0022] The module housing 26 may be made of a hard material such asaluminum. The module housing 26 is attached to the substrate 24 todefine an internally sealed cavity to store the components and othercircuitry for the electronic control module 20. For automobile uses, themodule housing 26 may also have outwardly extending flanges 32 to mountthe electronic control module 20 to an automobile (not shown).

[0023]FIG. 2 illustrates an exploded view of the electronic controlmodule 20 shown in FIG. 1. In one embodiment, the metallic substrate 24has a plurality of interconnect holes 34, a first surface 36, and asecond surface 38. The metallic substrate 24 may further have holes 40for connecting the connector housing 28 to the first surface 36 of themetallic substrate 24 by the use of mechanical fasteners such as screws41 (shown in FIG. 3).

[0024] The metallic substrate 24 may further have other holes 42 forconnecting metallic substrate 24 to the module housing 26 by the use ofmechanical fasteners such as screws 43. A further method is described inmore detail below for attaching the metallic substrate 24 to the modulehousing 26 to provide a hermetic seal. The metallic substrate 24 and themodule housing 26 may then define a hermetically sealed internal cavity44.

[0025]FIG. 3 illustrates a perspective view of the second surface 38 ofthe metallic substrate 24. The second surface 38 of the metallicsubstrate 24 is used for mounting components 46 and other circuitry ofthe electronic control module 20 within the sealed internal cavity 44.The exact components and circuitry are implementation specific but mayinclude devices such as transistors, processors, and memory. As those ofordinary skill will appreciate, the method and device described hereineliminates the need for wire bonds to connect the interconnects 30 tothe components 46 and other circuitry. Thus, the manufacturing processis less complex and the assembly costs are reduced.

[0026] As illustrated in FIG. 2, each of the plurality of electricallyconductive interconnects 30 extend through a separate interconnect hole34 in the metallic substrate 24. As illustrated in FIG. 3, each of theinterconnects 30 are attached to the metallic substrate 24. Inparticular, as will be explained in more detail below, the interconnects30 are attached to an electrically insulating layer of the metallicsubstrate 24 by a solderable coating and a solder.

[0027] FIGS. 4A-4F illustrate a suitable method for securing theelectrically conductive interconnects 30 to the metallic substrate 24.FIG. 4A is a cross sectional view of a single sheet of metallicsubstrate 24. As mentioned above, the metallic substrate 24 has a firstsurface 36 and a second surface 38.

[0028] As shown in FIG. 4B, the method further includes forming aplurality of interconnect holes 34 in the metallic substrate 24. Eachinterconnect hole 34 is defined by an internal surface 46 of themetallic substrate 24 that extends from the first surface 36 to thesecond surface 38. The width of the interconnect holes 34 is slightlylarger than the width of the interconnects 30 and the geometric shape ofthe interconnect holes 34 is preferably the same as the interconnects30.

[0029] As shown in FIG. 4C, the method further includes applying anelectrically insulating layer 48 to the metallic substrate 24 includingat least the first surface 36, the second surface 38, and the internalsurface 46. In one embodiment, where the metallic substrate 24 is madeof aluminum, the insulating layer 48 is an oxidation layer formedthrough an anodization process. Anodization in this case then willprovide the dielectric between the interconnects 30 and the metallicsubstrate 24.

[0030] As shown in FIG. 4D, the method further includes applying, byfiring or curing, a solderable coating 50 to at least a portion of theinsulating layer 48 on the second surface 38 of the metallic substrate24. The solderable coating 50 may be applied around each interconnecthole 34. The solderable coating 50 may also run inside each interconnecthole 34. This step is necessary when the insulating layer 48 is notpractically solderable. For example, solder will not adhere to anodizedaluminum. Therefore, a solderable coating 50 is applied to the metallicsubstrate 24.

[0031] A suitable solderable coating 50 is a high temperature processedglass filled ink, such as Ferro 3350 from Ferro Corporation, that isfired by being exposed to a temperature of approximately 600° C. forapproximately 5 minutes. The high temperature processed glass ispreferably one that contains one or more of silver and copper. Thisallows the solderable coating 50 to also serve as the electricallyconductive traces that run between the interconnects 30 and thecomponents 46. In another embodiment, the solderable coating 50 may be alow temperature processed organic material, such as Dynaloy 350 fromDynaloy, Inc., that is cured by being exposed to a temperature ofapproximately 150° C. for approximately 10 minutes. Applying asolderable coating 50 to a portion of the insulation layer 48 permitsthe securing of the interconnects 30 to the metallic substrate 24.

[0032] As shown in FIG. 4E, the method further includes applying asolder 52 to at least a portion of the solderable coating 50 at or aboveeach interconnect hole 34. The solder 52 is used to bond theinterconnects 30 to the metallic substrate 24 within the interconnectholes 34. The solder 52 may be a solder paste that is preferablyscreened onto the portion of the solderable coating 50.

[0033] As shown in FIG. 4F, the method further includes inserting ainterconnect 30 within each interconnect hole 34 so that theinterconnect 30 comes in contact with the solder 52. In one embodiment,this is done by inserting the interconnects 30 from the first surface 36of the metallic substrate 24. Thereafter, the interconnects 30 aresolder bonded to the metallic substrate 24. This may be done byreflowing solder paste in a reflow oven.

[0034] The above steps may be done by a mechanical process or inconnection with an automated pick-and-place machine. As seen in theprocess described in FIGS. 4A-4F, the use of wire bonds is eliminatedwhich reduces the complexity of the assembly process. The electricallyconductive traces of the circuitry running to the components 46 may bedirectly masked onto the insulated metallic substrate 24 and to theinterconnects 30. Additionally, no special plating is required on themetallic substrate 24. Moreover, the process steps described aboveutilize conventional methods such that special equipment is notnecessary.

[0035] Further, it is noted that the above described method may providea hermetic seal at each of the interconnect holes 34 after theprocessing steps. The interconnect holes 34 are sealed by the solderablecoating 50 and solder 52. This is of particular interest in automotiveapplications where the electronic control module 20 may need to behermetically sealed. The benefit of the present invention is that itpermits the use of small through holes in the metallic substrate 24.Thus, the overall area for leaks is severely reduced.

[0036] In cases where a hermetically sealed module is needed, FIGS.5A-5C illustrate a method for securing the metallic substrate 24 to themodule housing 26. In one embodiment, the metallic substrate 24 is arelatively flat piece of metal as shown in FIG. 5A. An outer edge 60 ofthe metallic substrate 24 is mated with a groove 62 formed in the modulehousing 26.

[0037] It is preferable to use soldering methods for attaching themetallic substrate 24 to the module housing 26. Soldering methods arecheaper than welding and other known methods. Solder, however, will notbond directly to thermally conductive metallic materials such asaluminum. Accordingly, a new way to permit soldering has been found totake advantage of lower cost assembly methods.

[0038] To permit soldering in this application, as shown in FIG. 5B, themethod includes applying, by firing, a solderable coating 64 to at leasta portion of the outer edge 60 of the metallic substrate 24 and to atleast a portion of the groove 62 of the module housing 26. This step isnecessary when the metallic pieces to be attached are not practicallysolderable.

[0039] A suitable solderable coating 64 is a high temperature processedglass filled ink, such as Ferro 3350 from Ferro Corporation, that isfired by being exposed to a temperature of approximately 600° C. forapproximately 5 minutes. The high temperature processed glass ispreferably one that contains one or more of silver and copper. Applyinga solderable coating 64 to the portion of the outer edge 60 of themetallic substrate 24 and to the portion of the groove 62 of the modulehousing 26 permits the securing of the metallic substrate 24 to themodule housing 26.

[0040] In one embodiment, the method may further include a step ofapplying an outer insulating layer (not shown) to the metallic substrate24 and the module housing 26 prior to the step of applying, or firing,the solderable coating 64. Similar to the process described above, ifthe material used for the metallic substrate 24 and the module housing26 is aluminum, the insulating layer may be an oxidation layer thatformed through an anodization process.

[0041] As shown in FIG. 5C, the outer edge 60 of the metallic substrate24 is joined with the groove 62 of the module housing 26 to form a joint66. The method further includes applying a solder 68 at the joint 66between a portion of the outer edge 60 of the metallic substrate 24 anda portion of the groove 62 of the module housing 26. The solder 68 isused to bond the metallic substrate 24 and the module housing 26. Thesolder 68 will also form a hermetic seal for the electronic controlmodule 20. The solder 68 may be a solder paste that is preferablyscreened onto the portion of the solderable coating 64. Thereafter, thejoint 66 may be solder bonded by reflowing solder paste of the solder 68in a reflow oven.

[0042] What has been described is a method and apparatus for securing anelectrically conductive interconnect through a metallic substrate. Thepresent invention permits the use of less costly assembly methods thatcan be of particular interest in high volume production.

[0043] The above description of the present invention is intended to beexemplary only and is not intended to limit the scope of any patentissuing from this application. For example, the present discussion usedan electronic control module to illustrate the method and apparatus ofthe present invention. The present invention is also applicable to otherapplications that use a metallic substrate and may further apply toelectrically connecting circuits and components through multiplemetallic substrates. The present invention is intended to be limitedonly by the scope and spirit of the following claims.

What is claimed is:
 1. A method for securing an electrically conductiveinterconnect through a metallic substrate, the metallic substrate havinga first surface and a second surface, the method comprising the stepsof: forming a hole in the metallic substrate, the hole defined by aninternal surface of the metallic substrate that extends from the firstsurface to the second surface of the metallic substrate; applying anelectrically insulating layer to the metallic substrate including atleast the first surface, the second surface, and the internal surface;applying a solderable coating to at least a portion of the electricallyinsulating layer on the second surface of the metallic substrate aroundthe hole; applying a solder to at least a portion of the solderablecoating and above the hole; inserting the interconnect through the hole;and solder bonding the interconnect within the hole.
 2. The method ofclaim 1 wherein the metallic substrate is made of aluminum.
 3. Themethod of claim 2 wherein the step of applying the electricallyinsulating layer to the metallic substrate includes anodizing themetallic substrate to form an oxidation layer to the metallic substrate.4. The method of claim 1 wherein the step of applying the solderablecoating to at least the portion of the electrically insulating layerincludes firing a high temperature processed glass filled ink.
 5. Themethod of claim 1 wherein the step of applying the solderable coating toat least the portion of the electrically insulating layer includescuring a low temperature processed organic material.
 6. The method ofclaim 1 wherein the step of applying a solder to at least the portion ofthe solderable coating includes applying a solder paste.
 7. The methodof claim 1 wherein the step of inserting the interconnect through thehole includes inserting the interconnect from the first surface of themetallic substrate.
 8. The method of claim 1 wherein the step of solderbonding the interconnect within the hole includes placing theinterconnect such that it comes in contact with the solder applied abovethe hole; and reflowing the solder in a reflow oven.
 9. A modulecomprising: a connector having a connector housing and a plurality ofelectrically conductive interconnects; and a metallic substrate having aplurality of holes, a first surface, a second surface, and anelectrically insulating layer, the insulating layer formed on at leastthe first surface, the second surface, and within the plurality ofholes; wherein each of the plurality of interconnects extend through aseparate hole in the metallic substrate and attached to the insulatinglayer of the metallic substrate by a solderable coating and a solder.10. The module of claim 9 further having an internal cavity that ishermetically sealed, the connector housing attached to the first surfaceof the metallic substrate, and the second surface of the metallicsubstrate facing the internal cavity.
 11. The module of claim 9 whereinthe metallic substrate is made of aluminum.
 12. The module of claim 11wherein the electrically insulating layer is an oxidation layer formedby an anodization process.
 13. The module of claim 9 wherein thesolderable coating is a high temperature glass filled ink containing oneor more of silver and copper.
 14. The module of claim 9 wherein thesolderable coating is a low temperature processed organic materialcontaining one or more of silver and copper.
 15. An electronic controlmodule for a vehicle comprising: a connector having a connector housingand a plurality of electrically conductive interconnects; a metallicsubstrate having a plurality of holes, a first surface, a secondsurface, and an electrically insulating layer, the insulating layerformed on at least the first surface, the second surface, and within theplurality of holes; a means for securing the plurality of interconnectsto the metallic substrate to provide a hermetic seal; and a means forelectrically connecting the plurality of interconnects to components andcircuitry on the metallic substrate without the use of wire bonds. 16.The electronic control module of claim 15 further having an internalcavity that is hermetically sealed, the connector housing attached tothe first surface of the metallic substrate, and the second surface ofthe metallic substrate facing the internal cavity.
 17. The electroniccontrol module of claim 15 wherein the metallic substrate is made ofaluminum.
 18. The electronic control module of claim 17 wherein theelectrically insulating layer is an oxidation layer formed by ananodization process.
 19. The electronic control module of claim 15wherein the means for securing the plurality of interconnects to themetallic substrate includes a solderable coating and a solder.
 20. Theelectronic control module of claim 19 wherein the solderable coating isa high temperature glass filled ink containing one or more of silver andcopper.
 21. The electronic control module of claim 19 wherein thesolderable coating is a low temperature processed organic materialcontaining one or more of silver and copper.